Six kinds of consolidants for the lime plaster that needed in-situ protection in ancient building were prepared by diammonium phosphate（DAP）， ethyl orthosilicate and nano-calcium hydroxide solution， and their consolidation effects were evaluated by compatibility and effectiveness. The results show that the consolidant with the best comprehensive performance is 0.1 mol/L DAP solution with 5%（by volume） ethanol. The lime plaster consolidated by the above consolidant generates more chemically stable hydroxyapatite mineral， hence its surface density increases， its color changes in line with the requirement of cultural relic protection， and the risk of residual N and P elements is small. It indicates that the compatibility of the consolidant is good. The capillary water absorption capacity， surface cohesion， dynamic elastic modulus and compressive strength of the above consolidated lime plaster are significantly improved， which indicates the effectiveness of the consolidant.